The general aim of the investigation is to determine some of the factors that influence axonal growth, either during regeneration following injury or during ontogenetic development. Of special interest is the process of regeneration in some lower vertebrates which, unlike mammals, have retained into adult life the capacity for repair of damage to the central nervous system. The basic questions that underlie this study are (1) what are the stimuli that initiate axonal growth, (2) what factors influence the rate of elongation of the growing axon, and (3) what interactions may occur between such an axon and the cells with which it comes in contact. The answers to these questions are important for an understanding of the developmental dynamics of the embryonic and neonatal nervous system, and the prospect is that they may provide clues to procedures for promoting the repair of damaged nervous tissue. Specific areas to be investigated include the mechanisms of axonal transport of materials in normal and regenerating nerve cells; the characteristics of protein metabolism in nerve cells undergoing axonal growth during regeneration or development, and the transfer of materials from one nerve cell to another. Experiments are to be performed mainly on the visual systems of fish and small mammals, and will involve the use of radioactive tracers.